The present invention relates to somatic mutations in the Multiple Tumor Suppressor (MTS) gene in human cancers and their use in the diagnosis and prognosis of human cancer. The invention further relates to germline mutations in the MTS gene and their use in the diagnosis of predisposition to cancer, such as melanoma, ocular melanoma, leukemia, astrocytoma, glioblastoma, lymphoma, glioma, Hodgkin's lymphoma, multiple myeloma, sarcoma, myosarcoma. cholangiocarcinoma, squamous cell carcinoma, CLL, and cancers of the pancreas, breast, brain, prostate, bladder, thyroid, ovary, uterus, testis, kidney, stomach, colon and rectum. The invention also relates to the therapy of human cancers which have a mutation in the MTS gene, including gene therapy, protein replacement therapy and protein mimetics. Finally, the invention relates to the screening of drugs for cancer therapy.
The publications and other materials used herein to illuminate the background of the invention, and in particular, cases to provide additional details respecting the practice, are incorporated herein by reference, and for convenience are referenced in the following text and respectively grouped in the appended List of References.
The genetics of cancer is complicated, involving multiple dominant, positive regulators of the transformed state (oncogenes) as well as multiple recessive, negative regulators (tumor suppressor genes). Over one hundred oncogenes have been characterized. Fewer than a dozen tumor suppressor genes have been identified, but the number is expected to increase beyond fifty (Knudson, 1993).
The involvement of so many genes underscores the complexity of the growth control mechanisms that operate in cells to maintain the integrity of normal tissue. This complexity is manifested in another way. So far, no single gene has been shown to participate in the development of all, or even the majority of human cancers. The most common oncogenic mutations are in the H-ras gene, found in 10-15% of all solid tumors (Anderson et al., 1992). The most frequently mutated tumor suppressor gene is the p53 gene, mutated in roughly 50% of all tumors. Without a target that is common to all transformed cells, the dream of a "magic bullet" that can destroy or revert cancer cells while leaving normal tissue unharmed is improbable. The hope for a new generation of specifically targeted antitumor drugs may rest on the ability to identify tumor suppressor genes or oncogenes that play general roles in control of cell division.
The tumor suppressor genes, which have been cloned and characterized, influence susceptibility to: 1) retinoblastoma (RB1); 2) Wilms' tumor (WT1); 3) Li-Fraumeni (TP53); 4) Familial adenomatous polyposis (APC); 5) Neurofibromatosis type 1 (NF1); 6) Neurofibromatosis type 2 (NF2); 7) von Hippel-Lindau syndrome (VHL); and 8) Multiple endocrine neoplasia type 2A (MEN2A).
Tumor suppressor loci that have been mapped genetically but not yet isolated include genes for: Multiple endocrine neoplasia type 1 (MEN1); Lynch cancer family syndrome 2 (LCFS2); Familial breast cancer (BRCA1); Neuroblastoma (NB); Basal cell nevus syndrome (BCNS); Beckwith-Wiedemann syndrome (BWS); Renal cell carcinoma (RCC); Tuberous sclerosis 1 (TSC1); and Tuberous sclerosis 2 (TSC2). The tumor suppressor genes that have been characterized to date encode products with similarities to a variety of protein types, including DNA binding proteins (WT1), ancillary transcription regulators (RB1), GTPase activating proteins or GAPs (NF1), cytoskeletal components (NF2), membrane bound receptor kinases (MEN2A), and others with no obvious similarity to known proteins (APC and VHL).
In many cases, the tumor suppressor gene originally identified through genetic studies has been shown in some sporadic tumors to be lost or mutated. This result suggests that regions of chromosomal aberration may signify the position of important tumor suppressor genes involved both in genetic predisposition to cancer and in sporadic cancer.
One of the hallmarks of several tumor suppressor genes characterized to date is that they are deleted at high frequency in certain tumor types. The deletions often involve loss of a single allele, a so-called loss of heterozygosity (LOH), but may also involve homozygous deletion of both alleles. For LOH, the remaining allele is presumed to be nonfunctional, either because of a preexisting inherited mutation, or because of a secondary sporadic mutation.
Melanoma is a common cancer afflicting one in every hundred Americans (American Cancer Society, 1992). Environmental influences, such as exposure to ultraviolet light, play a large role in melanoma incidence, but heredity is also a contributing factor. A gene for familial melanoma, MLM, has been mapped to chromosome 9p21 (Cannon-Albright et al., 1992; Nancarrow et al., 1993; Gruis et al., 1993; Goldstein et al., 1994). Possession of a single predisposing allele at the MLM locus increases the probability that an individual will develop melanoma by up to approximately 50-fold. MLM belongs to the growing family of suspected tumor suppressor genes.
Predisposition to melanoma is inherited as a dominant Mendelian trait, yet predisposing mutations in MLM are thought to act as somatic recessive alleles in the manner originally proposed by Knudson (1971). In a predisposed individual who carries one wild-type and one mutant MLM allele, dividing cells undergo secondary mutational events that involve loss or inactivation of the wild-type copy of MLM, thereby uncovering the inherited mutant MLM allele. Conversely, a single wild-type copy of the gene prevents the onset of malignancy.
Chromosomal aberrations in the vicinity of MLM at 9p21 have been extensively characterized in several different tumor types, including glioma cell lines, non-small cell lung lines and acute lymphoblastic leukemia lines (Olopade et al., 1992; Olopade et al., 1993; Lukeis et al., 1990; Diaz et al., 1988; Middleton et al., 1991; Fountain et al., 1992; Cheng et al., 1993; James et al., 1993). Thus, based on the frequency of 9p21 chromosomal abnormalities in non-melanoma tumor cells, it is probable the MLM region contains a gene (or genes) that participates at least in the progression of several different tumor types. These events involve LOH as well as a high frequency of homozygous deletion.
Cells in tissues have only three serious options in life--they can grow and divide, not grow but stay alive, or die by apoptosis. Tumors may arise either by inappropriate growth and division or by cells failing to die when they should. One of the mechanisms for controlling tumor growth might involve direct regulation of the cell cycle. For example, genes that control the decision to initiate DNA replication are attractive candidates for oncogenes or tumor suppressor genes, depending on whether they have a stimulatory or inhibitory role in the process. Progression of eukaryotic cells through the cell cycle (G.sub.1, S, G.sub.2 and M phases) is governed by the sequential formation, activation and subsequent inactivation of a series of cyclin/cyclin-dependent kinase (Cdk) complexes. Cyclin D's/Cdk2,4,5, Cyclin E/Cdk2, Cyclin A/Cdk2 and Cyclin B/A/Cdk2 have been shown to be involved in this process. Cyclin D's and Cdk2, Cdk4 and Cdk5 have been implicated in the transition from G.sub.1 to S; that is, when cells grow and decide whether to begin DNA replication. Additional cell cycle control elements have recently been discovered. These elements are inhibitors of Cdks (Cdk inhibitors, CkI), and include Far1, p21, p40, p20 and p16. (Marx, 1994; Nasmyth & Hunt, 1993).
Recently, several oncogenes and tumor suppressor genes have been found to participate directly in the cell cycle. For example, one of the cyclins (proteins that promote DNA replication) has been implicated as an oncogene (Motokura et al., 1991; Lammie et al., 1991; Withers et al., 1991; Rosenberg et al., 1991), and tumor suppressor Rb interacts with the primary cyclin-binding partners, the Cdks (Ewen et al., 1993). Identification of a melanoma susceptibility locus would open the way for genetic screening of individuals to assess, for example, the increased risk of cancer due to sunlight exposure. The MTS may also predispose to a large number of other cancer sites, including but not limited to, leukemia, astrocytoma, glioblastoma, lymphoma, glioma, Hodgkin's lymphoma, multiple myeloma, sarcoma, myosarcoma, cholangiocarcinoma, squamous cell carcinoma, CLL, and cancers of the pancreas, breast, brain, prostate, bladder, thyroid, ovary, uterus, testis, kidney, stomach, colon and rectum. In addition, since MTS influences progression of several different tumor types, it should be useful for determining prognosis in cancer patients.
Thus, MTS may serve as the basis for development of very important diagnostic tests, one capable of predicting the predisposition to cancer, such as melanoma, ocular melanoma, leukemia, astrocytoma, glioblastoma, lymphoma, glioma, Hodgkin's lymphoma, multiple myeloma, sarcoma, myosarcoma, cholangiocarcinoma, squamous cell carcinoma, CLL, and cancers of the pancreas, breast, brain, prostate, bladder, thyroid, ovary, uterus, testis, kidney, stomach, colon and rectum, and one capable of predicting the prognosis of cancer. Furthermore, since MTS is involved in the progression of multiple tumor types, MTS may provide the means, either directly or indirectly, for a general anti-cancer therapy by virtue of its ability to suppress tumor growth. For example, restoration of the normal MTS function to a tumor cell may transmute the cell into non-malignancy.